A semiconductor photodetector is a semiconductor device configured to operate using a principle that electric current flows in response to application of light. In a semiconductor-based photodetector, a depletion region is generated by separation of holes and electrons in the semiconductor upon irradiation with light such that electric current flows therein due to the flow of electrons.
Generally, the photodetector is manufactured using a silicon semiconductor, a nitride semiconductor, and the like, all of which have energy band-gaps suitable for detection of light such as UV light. Such a photodetector can exhibit peak response at various wavelengths according to characteristics of the semiconductor. For example, a photodetector including a nitride semiconductor exhibits peak response at various wavelengths depending upon the composition ratio of constituent elements of a light absorption layer. Furthermore, in the nitride-based photodetector, a cut-off inclination of response according to wavelength differs depending upon the composition ratio of the constituent elements, and a decrease inclination of response according to decrease in wavelength also differs depending upon the composition ratio of the constituent elements.
Particularly, a semiconductor UV detection element can be applied to various fields including commerce, medicine, the military industry and communication, and thus is very important in such fields. Particularly, among GaN-based UV detection elements, Schottky junction type, metal-semiconductor-metal (MSM) type, and PIN type UV detection elements are generally used in the art. Although these GaN-based UV detection elements do not secure reproducibility and characteristics of a p-type AlGaN layer having a high Al content, the Schottky junction type UV detection element does not require growth of the p-AlGaN layer and thus is preferred due to a simple manufacturing process thereof. However, since the Schottky junction type UV detection element is based on Schottky characteristics between a semiconductor layer and a metal layer, the Schottky junction type UV detection element is more vulnerable to electrostatic discharge (ESD) than the PIN type UV light detection element.
In addition, in a UV detector in which an integrated circuit having a function of an analog-digital converter (ADC) is mounted on a housing and a UV detection element is bonded thereto, digital signals can be directly output from the housing. Here, since the integrated circuit is affected by UV light, visible light and infrared light, an output signal from the UV detector contains an output signal from the integrated circuit, thereby providing an inaccurate UV detection signal. This problem becomes apparent upon detection of UV light having a certain wavelength from sunlight.
On the other hand, UV light has a wavelength of 10 nm to 400 nm, which is shorter than the wavelength of a violet color, which has the shortest wavelength in the wavelengths of visible light, and has high energy to cause chemical reaction or a negative influence on human health. The UV light can be classified into many kinds depending upon wavelengths thereof and can be naturally obtained from sunlight or artificially obtained from a UV lamp and the like.
In sunlight, about 90% of UV light reaching the ground falls within the UVA wavelength band, and about 10% of the UV light falls within the UVB wavelength band. UV light in the UVC wavelength band is absorbed in the ozone layer and the atmosphere and substantially does not reach the ground. Artificial UV light is generated from UVA, UVB, and UVC lamps.
UVA light has a wavelength of 320 nm to 400 nm and is also referred to as life UV light to which persons are exposed in everyday life. The UVA light is encountered regardless of weather and reaches the dermal layer inside the skin to affect collagen and elastin acting to maintain skin elasticity, and pigment cells, thereby accelerating skin aging, such as generation of fine wrinkles, loss of skin elasticity, and generation of freckles through pigmentation.
UVB light has a wavelength of 280 nm to 320 nm and is also referred to as leisure UV light since UVB light causes sunburn on the skin to generate pain and inflammation thereon when a person is exposed to the sun on the beach or the like for a long time. UVB light provides beneficial effects such as synthesis of vitamin D, psoriasis treatment, and the like when a person is suitably exposed thereto, and can cause skin cancer or cataracts when a person is excessively exposed thereto.
UVC light has a wavelength of 200 nm to 280 nm and substantially does not reach the ground due to absorption in the atmosphere. However, UVC light is known to be very detrimental to the human body due to very high energy thereof. UVC light is broadly known as sterilization UV light.
The UV index is an index representing the intensity of UV light obtained by integrating the McKinlay-Diffey erythemal action spectrum curve, which indicates spectral irradiance of sunlight and the degree of damage to skin in the wavelength range of about 285 nm to about 385 nm, as a weighting function according to wavelength. The UV index indicates an influence of solar UV light on the skin.
As such, since UV light can be very detrimental to the human body depending upon the degree of exposure, with significant increasing concern on health, use of UV blocking agents increases in order to secure protection from UV light, and a technique of allowing a user to receive information regarding UV notice/alert through a personal digital assistant such as a mobile phone or a technique of allowing a user to measure the UV index in real time through a UV sensor mounted on the personal digital assistant is developed and distributed.
Actually, although a smart phone released in 2014 is provided with a UV sensor to provide information regarding the UV index, this smart phone is configured to display a UV range using a silicon-based sensor configured to detect visible light due to various reasons, such as manufacturing convenience and cost, and is known to fail to provide advantageous effects to users.
In order to display the UV index, it is necessary to detect and display the UVB wavelength band. However, since the silicon-based sensor is configured to estimate the UV index based on the intensity of visible light and part of the UVA wavelength band instead of directly detecting UV light in the UVB wavelength band, a UV index measurement device including such a silicon-based UV sensor provides a significant error between the measured UV index and an actual UV index. Moreover, although the UV index measurement device inevitably employs an expensive filter, use of the filter causes increase in manufacturing costs and such a filter still has a problem of incomplete blocking of visible light.
Moreover, although an application program of a smart phone can be used in the related art, the application program has low usability due to user inconvenience by requiring a user to execute the application program to detect UV light after installing the application program, and cannot automatically calculate the UV index, thereby making it difficult to obtain secondary information based on the UV index, such as UV risk degree, UV exposure time, UV exposure accumulation time, vitamin D synthesis time, and the like, in real time.